1. Field of the Invention
The present invention relates to an image sensing device and an image sensing system.
2. Description of the Related Art
Image sensing devices have been recently used as two-dimensional image input devices mainly including digital still cameras and video camcorders or one-dimensional image reading devices mainly including facsimiles and scanners, and the demand for image sensing devices is rapidly increasing. CCD (Charge-Coupled Device) sensors and MOS sensors are used as such image sensing devices. As a typical example of such MOS sensors, CMOS sensors have been put to practical use.
Japanese Patent Laid-Open No. 2008-42825 discloses that, as shown in FIG. 2 of Japanese Patent Laid-Open No. 2008-42825, a pixel portion 10 of a solid-state image sensing device 1 has a photodiode 12 serving as a photoelectric conversion element, a memory group 14, and an amplifier 16. The memory group 14 includes N (N is an integer) memories serving as storage elements. Each memory holds and stores signal electric charges output from the photoelectric transducer as an analog quantity. The memory group 14 selectively reads out a signal from one or more memories of the N memories. The amplifier 16 amplifies the signal selectively read out from the memory group 14. Japanese Patent Laid-Open No. 2008-42825 describes that the memories of the memory group 14 may be MIM (Metal-Insulator-Metal) capacitances, as shown in FIG. 14 of Japanese Patent Laid-Open No. 2008-42825.
An image sensing device has an image sensing region and a peripheral region arranged on the periphery of the image sensing region. In some cases, this image sensing region is configured to include an effective region in which a plurality of effective pixels including photoelectric conversion units that are not shielded from light is arranged and an optical black region that is a region adjacent to the effective region and in which a plurality of optical black pixels including photoelectric conversion units that are shielded from light is arranged.
Here, the inventor of the present invention conceived of the idea of disposing an MIM element as a capacitance element between a light shielding layer and a wiring layer directly under the light shielding layer. This MIM element functions, for example, in a peripheral circuit, as a holding capacitance for holding signals output from the pixels or a clamp capacitance for generating differential signals between noise signals and optical signals output from the pixels.
In this case, in the peripheral region, the height of the light shielding layer from an upper surface of a semiconductor substrate is greater than in the case where the MIM element is not provided; therefore, also in the optical black region, the height of the light shielding layer from the upper surface of the semiconductor substrate is likely to be greater. This causes stray light from between the upper surface of the semiconductor substrate and the light shielding layer toward the optical black pixels to occur in the vicinity of a boundary between the effective region and the optical black region, and the optical black pixels thus cannot output reference signals of the correct black level.